1. Field of the Invention
This invention relates to an air-conditioning apparatus having at least one room unit (indoor side unit) and plural outdoor side units which are connected in parallel to an interunit pipe extending from the room unit.
2. Description of Related Art
A multiroom air-conditioning apparatus for simultaneously cooling or heating a plurality of rooms of a building has been generally known. This multiroom air-conditioning apparatus is disclosed in Japanese Laid-open Patent Application No. 2-85656, and is so constructed that a plurality of outdoor side units each having a compressor, an outdoor heat exchanger, etc. are arranged so as to be connected in parallel to an inter-unit pipe connected to each room unit. This type of multiroom air-conditioning apparatus has an advantage that realization of a large-capacity system can be promoted for such an apparatus.
This type of multiroom air-conditioning apparatus has been conventionally so designed that a refrigerant flow between each outdoor side unit and each indoor side unit (room unit) is controlled through closing and opening operations of a valve, and the closing and opening operations of each valve are carried out with an individual controller which is individually provided to each outdoor side unit. In this construction, alteration of the number of outdoor side units or indoor side units to be connected necessarily requires the control operation (program) of each outdoor side unit to be individually altered, or requires each of the individual controllers itself to be replaced by another. Therefore, the conventional multiroom air-conditioning apparatus has had a disadvantage that the individual controllers can not be fixedly used without modification or replacement in any status.
Further, in the conventional multiroom air-conditioning apparatus thus constructed, the same refrigerant flows in or out over plural outdoor side units which are arranged in parallel in the same system. Therefore, there occurs a problem that in a case where the refrigerant is partially trapped (naturally stocked) in an outdoor side unit located adjacently to an outdoor side unit in operation, the outdoor side unit in operation lacks the refrigerant, and a so-called "gas-lacking state" occurs in the outdoor side unit in operation.
In addition, in a case where a large amount of refrigerant concentratively flows into an outdoor side unit, there occurs a problem that surplus refrigerant is liable to be trapped in an outdoor heat exchanger, etc. of the outdoor side unit. For example, when the refrigerant is trapped in the outdoor heat exchanger in a cooling operation, liquefaction of the refrigerant is depressed because a heat-discharge area is reduced.
Further, in this type of multiroom air-conditioning apparatus having plural outdoor side units arranged in parallel, the air-conditioning operation is so controlled that the operation of some outdoor side units (compressors) is ceased when an air-conditioning load is reduced to a value lower than the total output of the compressors of the outdoor side units. In such a control operation, the output of the air-conditioning apparatus is required to be smoothly controlled over an air-conditioning load range of the minimum (zero) air-conditioning load to the maximum air-conditioning load.